The natural law is immutable and permanent throughout the variations of history; it subsists under the flux of ideas and customs and supports their progress. The rules that express it remain substantially valid. Even when it is rejected in its very principles, it cannot be destroyed or removed from the heart of man. It always rises again in the life of individuals and societies:
Theft is surely punished by your law, O Lord, and by the law that is written in the human heart, the law that iniquity itself does not efface.
Source: Catechism of the Catholic Church (Vatican.va)